let 1<=r<=n. A subset of{1,2....n} of cardinality "r" is chosen at random. How do i calculate the probability that 1 is an element of the chosen subset

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- October 19th 2008, 07:12 AMmath8553probability
let 1<=r<=n. A subset of{1,2....n} of cardinality "r" is chosen at random. How do i calculate the probability that 1 is an element of the chosen subset

- October 19th 2008, 09:58 AMPlato
- October 19th 2008, 10:16 AMvincisonfireReply
The number of subset of cardinality r is

and the number of those that doesn't contain 1 is as Plato told you.

The probability of taking a set that doesn't contain 1 is